Robert Makemson Guide to Astronomy in Jacksonville

Topocentric Positions Solar System Objects and Stars

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Topocentric Positions

 A system of celestial coordinates with its origin at a specific point on Earth's surface. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric (Earth-centered) coordinates is very small because most celestial objects are so far away. The Moon's position, however, can vary as much as 2 depending on where on Earth it is measured from, and, within the past few years, an observatory in Australia missed spotting an asteroid that passed close to Earth because it used geocentric rather than topocentric positions.

Topocentric Positions of Major Solar System Objects and Bright Stars

Be sure to read the Notes section (on this page beyond the two forms) for definitions and additional details on the data.

Form A - U.S. Cities or Towns

Universal Time (UT1)

(1 to 9999)

The place name you enter above must be a city or town in the U.S. The place's location will be retrieved from a file with over 22,000 places listed. Either upper- or lower-case letters or a combination can be used. Spell out place name prefixes, as in "East Orange", "Fort Lauderdale", "Mount Vernon", etc. The only exception is "St.", which is entered as an abbreviation with a period, as in "St. Louis". You need only enter as many characters as will unambiguously identify the place.

(-90 to 10999) meters

If the observer's height above sea level is known, you may enter it here. If unknown, sea level will be assumed.

Form B - Locations Worldwide

Universal Time (UT1)

(1 to 9999)

The place name you enter above is merely a label for the table header; you can enter any identifier, or none (avoid using punctuation characters). The data will be calculated for the longitude and latitude you enter below.

Longitude:
Latitude:

(-90 to 10999) meters

If the observer's height above sea level is known, you may enter it here. If unknown, sea level will be assumed.

Need coordinates? Try NGA's GEOnet Names Server (GNS).
Need U.S. coordinates? Try the USGS Geographic Names Information System (GNIS).